text: The original method of protein skimming, running pressurized air through a diffuser to produce large quantities of micro bubbles, remains a viable, effective, and economic choice, although newer technologies may require lower maintenance.  The air stone is most often an oblong, partially hollowed block of wood, most often of the genus Tilia. The most popular wooden air-stones for skimmers are made from limewood (Tilia europaea or European limewood) although basswood (Tilia americana or American Linden), works as well, may be cheaper and is often more readily available. The wooden blocks are drilled, tapped, fitted with an air fitting, and connected by air tubing to one or more air pumps delivering at least 1 cfm.  The wooden air stone is placed at the bottom of a tall column of water. The tank water is pumped into the column, allowed to pass by the rising bubbles, and back into the tank. To get enough contact time with the bubble, these units can be many feet in height.
  Air stone protein skimmers may be constructed as a DIY project from pvc pipes and fittings at low cost  [http://www.angelfire.com/ok/dog1/skimmer.html] [http://www.hawkfish.org/snailman/diy8inskimmer.htm] and with varying degrees of complexity [https://web.archive.org/web/20121225063946/http://ozreef.org/diy_plans/protein_skimmers/air_stone_protein_skimmer.html].
  Air stone protein skimmers require powerful air pumps which are often power hungry, loud, and hot, leading to an increase in the aquarium water temperatures. While this method has been around for many years, due to more efficient technologies emerging, many regard it as inefficient current uses in larger systems or systems with large bio-loads.